1. Field of the Invention
The present invention relates to an optical module, and particularly to an optical module including a semiconductor optical device in which a laser section and a mirror are monolithically integrated.
2. Description of the Related Art
To achieve size reduction and cost reduction, decrease in power consumption, and increase in capacity of an optical module, it is desired to improve an optical waveguide technology for integrating a large number of optical functions in a single device. To this end, a variety of types of research and development on silicon photonics (hereinafter referred to as SiP) technologies have been recently conducted. The SiP technology is a technology extended from a CMOS process developed for an electrical integrated circuit to formation of an optical waveguide circuit. The SiP technology allows a large number of optical functions to be integrated in optical interconnection. However, to further improve the SiP technology, it is desirable to form a light source (semiconductor laser) on a silicon substrate in such a way that the light source is integrated with the substrate. Materials that can be grown in the form of crystal on a silicon substrate and allows laser oscillation have, however, not been known at a practical level, and no laser source has therefore so far been integrated on a silicon substrate. It is therefore necessary to separately provide a light source, and a technology for coupling an InGaAs semiconductor laser with an SiP device in a hybrid implementation process is, for example, used. The SiP device used herein is a device in which an optical waveguide circuit is formed on an Si substrate. In the formation process, it has been known that the coupling between the semiconductor laser and the SiP device is achieved by a grating coupler formed in a surface layer of the SiP device. The grating coupler is an optical part that uses Bragg reflection to convert the propagating direction of light with which the surface is irradiated into a direction in a plane of the device, focusing the light, and efficiently coupling the focused light with an optical waveguide extending in the plane. Use of the grating coupler allows evaluation of the optical device in a wafer state and is therefore suitable for volume production and cost reduction.